Conventional tape printing devices, provided with a dot print type printing mechanism include a keyboard for inputting characters having attributes such as upper case, lower case, boldfacing etc., a display unit, and a control unit comprising a character generator and text memory means. The character generator and text memory means store the dot pattern data for the alphanumeric characters. This allows characters input from the keyboard to be printed on a recording medium by the printing means.
In the conventional art, the control unit consists of an index table in which the character codes are stored. The dot pattern data for characters having one or more attributes are stored in the index table. Thus, for example, the upper case characters input from the keyboard will address the upper case dot pattern data stored in the index table. Similarly the lower case characters will address the lower case dot pattern data stored in the index table. Thus a character string consisting of characters having a first attribute arid characters having a second attribute will address the dot pattern data stored in the index table corresponding to the characters having the respective attributes. In other words, a character string consisting of lower case and upper case characters will address both the lower case and upper case dot pattern data stored in the index table. This data is then read out, and transferred to the printing means to produce the output on the recording medium.
In the conventional tape printing device, after a character string consisting of characters having more than one attribute has been input, there may be the need to modify the string such that all of the characters to be output have the same attribute. However, since the input characters address their respective dot pattern data, a change to another attribute requires that the original character be deleted and the new character be input. Thus, for example, if a character string having lower and upper case characters has been input, there may be the need to modify the string such that all of the characters are either upper case or lower case. However, since the input characters address their respective dot pattern data, a change to the opposite ease requires that the original character be deleted and the new character be input.
Also, the original character string must be separately stored in the memory if it is to be used later. Therefore, in the conventional tape printing device, changing a character string consisting of characters having more than one attribute, to a character string having only one attribute is a time consuming and inefficient process.